Continuous drum vacuum filter

ABSTRACT

A continuous drum vacuum filter wherein the drum, rotatable about its axis, has on its working surface cells whose external sides are formed by a filtering material. The cells are connected by means of ducts to the movable part of a valve installed coaxially with the drum and serving to connect the cells in the required sequence to suction and compressed air lines during rotation of the drum. The fixed part of the valve has an overflow channel so ensuring communication of a cell emerging from the suspension with a cell submerging into the suspension that overflowing of the filtrate from the former cell to the latter is ensured.

United States Patel Nikolai Alexandrovlch Bun-tsev Inventor ulltsaDagestans Kaye 20, ltv. l2, Sverdlovsk, U.S.Shk.

Appl. No. 48,106

Filed June 22, 1970 Patented Dec. 14, 19711 CONTINUOUS DRUM VACUUMlFllLTlER [56] References Cited UNlTED STATES PATENTS 3,363,774 l/l968Luthi 210/404 Primary Examiner-Reuben Friedman Assistant ExaminerT. A.Granger AttorneyWaters, Roditi, Schwartz & Nissen ABSTRACT: A continuousdrum vacuum filter wherein the drum, rotatable about its axis. has onits working surface cells whose external sides are formed by a filteringmaterial. The cells are connected by means of ducts to the movable partofa valve installed coaxially with the drum and serving to connect thecells in the required sequence to suction and compressed air linesduring rotation of the drum. The fixed part of the valve has an overflowchannel so ensuring communication ofa cell emerging from the suspensionwith a cell submerging into the suspension that overflowing of thefiltrate from the former cell to the latter is ensured.

- Pmmmd Demo 14,, 1971 3 Sheets-Sheet w CONTENUOUS DRUM VACUUM MILTIERThe present invention relates to apparatuses for separating suspensionsinto the liquid and solid phases and, more particularly, to continuousdrum vacuum filters used in the chemical. food, ore concentration,medicine and other industries.

Known in the prior art are continuous drum vacuum filters comprising adrum rotatable about its own axis, whose working cylindrical surface isformed by a filtering material, for example, filter fabric, and isdivided along the circumference into a plurality of cells; a trough witha suspension into which the drum is partly submerged; a device forremoving the precipitate from the external surface of the filteringmaterial; a valve consisting of a movable and a fixed parts whose endsare lapped and pressed against each other. The movable part of the valveis secured on the end part of the drum and revolves together with it. ithas orifices, each of which is connected by means of ducts to thecorresponding cell of the drum. The fixed part of the valve is anannular box divided into a number of separate chambers, some of whichcommunicate with a vacuum and others with a source of compressed air.The chambers communicating with the vacuum form zones of filtration,washing and drying of the precipitate on the drum. The chamberscommunicating with the source of compressed air are zones for separatingthe precipitate from the filtering material and regeneration of thefiltering material.

Upon rotation of the drum each of its cells alternatively communicateswith all the said valve chambers.

The valve chambers are so arranged that each cell upon being submergedinto the suspension communicates with the compressed air line. Thecompressed air flows into the cell and, upon passing through thefiltering material, regenerates it. Then each cell communicates with thevacuum, and at the expense ofthe rarefaction in the cell the filtrate issucked from the trough into the cell through the filtering material. Thefiltrate is sucked into the cell before the latter moves out of thesuspension.

A disadvantage of these known vacuum filters, however, consists in thatthe regeneration of the filtering material in them is performed by meansof compressed air, which does not ensure sufficiently completeregeneration of the filtering material. This is explained by the factthat the compressed air does not blow through the fine capillaries, butpasses only through the course capillaries of the filtering material,without removing from the capillaries separate particles of the solidphase retained by the forces of surface tension. As a result thecapillaries are rapidly clogged, and the rate of filtration sharplydecreases. The result is that the mean output of these vacuum filters isconsiderably lower than the initial one. An increase of the zone ofregeneration of the filtering material does not improve regeneration,but, on the contrary, leads to the additional clogging of thecapillaries of the filtering material by the minutes! bubbles of air, asa result of which the resistance to filtration grows and additionalconditions are created for clogging of the filtering material with solidparticles. This shortcoming, besides reducing the output of the filter,leads to an increase in the consumption of the filtering material.

There are also known continuous drum vacuum filters whose design issimilar to that of the filters described above, wherein regeneration ofthe filtering material is performed by the filtrate, i.e., by the liquidfiltered in the course of operation of the filter. The fixed part of thevalve of these filters has such an arrangement of the chambers whichensures communication of a cell with the vacuum at the beginning of itssubmergence into the suspension. The cell is filled with the filtrate inan amount sufficient for ensuring regeneration of the filteringmaterial. At the moment when the cell is in its lowest position, and itsfiltering surface is almost horizontal and is completely covered by thefiltrate, compressed air is fed into the cell through the valve. Thisair forces out the filtrate from the cell through the filtering materialinto the trough and thus regenerates the material; after this the cellis again brought into communication with the vacuum, and filtrationproper takes place.

Owing to the use of liquid regeneration of the filtering material, thesevacuum filters do not have the shortcomings of the vacuum filters withair regeneration described above. The known vacuum filters with liquidregeneration, however, have a very small zone of filtration, equal to orless than half the angle of submergence of the drum into the suspension,regardless of its size. The other half of the angle of submergence isused for sucking the filtrate required for regeneration of the filteringmaterial into the cell and carrying out regeneration in the wayindicated above.

Owing to this shortcoming such filters can be employed only for thefiltration of easily filtered suspensions, where a large zone offiltration is not required, and are mainly used for the filtration ofsodium bicarbonate (soda).

A particular object of the present invention is to provide such acontinuous drum vacuum filter with regeneration of the filteringmaterial by the countercurrent of the liquid wherein the zone offiltration will be increased by reducing the zone of regeneration, whichwill make it possible to considerably expand the field of application ofvacuum filters with liquid regeneration.

This object is achieved by designing a continuous drum vacuum filtercomprising a drum rotatable about its own axis and having cells arrangedon its working surface, the external sides of the cells being formed byfiltering material, said cells being connected by means of ducts with amovable part of a valve installed coaxially with the drum and serving toconnect the cells during rotation of the drum in the required sequencewith suction and compressed air lines, a trough for a suspension inwhich the drum is partly submerged, and a device for removing theprecipitate from the external surface of the filtering material, whereina fixed part of the valve is provided, according to the presentinvention, with an overflow channel for connecting the cells emergingfrom the suspension with the cells submerging into the latter, thischannel ensuring overflowing of the filtrate from the former cells tothe latter ones. This results in rapid filling of a cell with thefiltrate required for regeneration by the filtering material, owing towhich the regeneration can be performed immediately after submersion ofthe cell into the suspension, and the zone of regeneration occupies aninsignificant part of the angle of submergence of the drum in thesuspension, while the zone of filtration is considerably extended.

in vacuum filters with a great angle of submergence of the drum in thesuspension it is preferable to provide the cells with accumulatingpockets for the suspension.

The nature of the present invention will become more fully apparent froma consideration of the following description of an exemplary embodimentthereof, taken in conjunction with the accompanying drawings, in which:

FIG. l is a schematic sectional view of a continuous drum vacuum filteraccording to the invention;

H6. 2 is a sectional view of a valve according to the invention;

H6. 3 is a deeply submerged drum vacuum filter according to theinvention;

FIG. 4 is a diagram showing the operation of the drum vacuum filter ofH0. 1;

FIG. 5 is a diagram showing the operation of the drum vacuum filter ofFIG. 2;

FIG. 6 is the same.

The continuous drum vacuum filter comprises drum 1 (FIG. 1) with aplurality ofcells 2.

Drum l is provided with a drive (not shown) for ensuring rotation ofdrum 1 about its own axis. Drum l is partly submerged in trough 3containing the suspension which is to be filtered. Mixer 4 is installedin trough 3. The vacuum filter is also provided with device 5 forremovingthe precipitated and with a valve installed coaxially with druml and having fixed part 6 and movable part '7 (FIGS. 1 and 2) whose endsare lapped and pressed against each other. Movable part 7 of the valveis secured on the end part of drum 1 (FIG. 1) and rotates together withit.

On its external cylindrical surface the drum is provided with drainagegrate 8 (FIG. 1) which is covered with a filtering medium, for example,filter fabric or some other filtering material.

Each cell 2 is provided with two ducts 9 and 10. Duct 9 passes at thefront wall of cell 2 in the direction of rotation of drum 1 (thedirection of rotation of drum 1 is shown in FIG. 1 by arrow A), and ductat the rear wall of cell 2. In the longitudinal direction of drum 1 eachcell 2 may have several ducts 9 and several ducts 10. The ends of ducts9 and 10 are connected to movable part 7 of the valve, the ends of ducts9 and the ends of ducts 10 being on concentric circles of differentdiameters relative to the center of drum 1.

Movable part 7 of the valve is provided with orifices 11 for connectingit to ducts 9 and 10. The number of orifices 11 in each concentric rowis equal to the number of cells 2.

Ducts 9 and 10 serve not only for connecting cells 2 to movable part 7of the valve, but also for accumulating the filtrate in an amountnecessary both for regeneration of the filtering material and forensuring a hydraulic seal for the compressed air fed into cell 2 in theprocess of regeneration. If the deeply submerged drum vacuum filtershown in FIG. 3 is used for filtration, the cells may have accumulatingpockets 12 in which the required amount of suspension is retained incell 2 when it emerges from thesuspension.

Fixed part 6 (FIG. 1) of the valve is provided with chamber 13 connectedto a vacuum line for filtration proper, chamber 14 connected to acompressed air line for regeneration purposes, chamber 15 communicatingwith the atmosphere through control valve 16, and overflow channel 17.Channel 17 is so designed that one end thereof is disposed opposite arow of orifices 11 arranged on one of the concentric circles of movablepart 7 of the valve, and the other end is opposite a row of orifices 11arranged on another concentric circle of movable part 7, therebyconnecting ducts 10 of each cell 2 emerging from the suspension to ducts9 of each cell 2 submerging into the suspension.

Chambers 13, 14 and 15 of fixed part 6 of the valve are separated fromone another by partitions which have such a shape that they can closeduct 10 of each cell 2 when it emerges from the suspension to ensuremore complete filling of the space of cell 2 and ducts 9 and 10 with thefiltrate, and also duct 9 (FIG. 3) of the cell submerging into thesuspension upon regeneration of the filtering material. This lattercondition is not obligatory for filters with a small angle ofsubmergence of drum 1 into the suspension (FIG. 1), when compressed aircan be supplied into ducts 9 and 10.

The alternatives of arrangement of the chambers described above are notthe only ones. The chambers of fixed part 6 of the valve, ducts 9 and I0and channel 17 can be disposed in any other way ensuring rapidoverflowing of the filtrate from cell 2 emerging from the suspensioninto cell 2 submerging into the suspension.

The drawings and the specification also do not describe other possiblechambers in fixed part 6 of the valve, for example. chambers for removalof the washing liquid, for drying the precipitate and blowing air overit during its removal, since they are of no importance for the presentinvention.

The drum vacuum filter operates as follows.

Drum 1 (FIG. 1) of the filter rotates about its horizontal axis in thedirection shown by arrow A. Movable part 7 of the valve, which issecured on the end of drum 1, turns with respect to fixed part 6 of thevalve and consecutively connects each cell 2 of drum 1 to all thechambers of fixed part 6 of the valve.

As a result each cell 2 consecutively passes through: filtration zone to(FIGS. 1 and 2), the zone of feeding the filtrate through overflowchannel 17 from cell 2 emerging from the suspension into cell 2submerging into the suspension; other zones not indicated in thedescription, including the zone where the precipitate is removed fromthe drum; the zone of filling cell 2 with filtrate through overflowchannel 17; and the zone of regeneration of the filtering material.

FIG. 4 shows the positions of cell 2 of the vacuum filter depicted inFIG. 1 when it passes through the zones listed above. The suspensionfrom cell 2b flows through overflow channel 17 into cell 20. In cell 2cthe filtering material is regenerated by the counter current of theliquid, while in cell 2d the cell is filled with filtrate during thefiltering process. FIGS. 5 and 6 show the same positions of cell 2'forthe deeply submerged vacuum filter depicted in FIG. 3.

In the zone of filtration proper (on the angle (0) cell 2 is connectedby ducts 9 and 10 to vacuum chamber 13 (FIG. 3). The filtrate suckedinto cell 2 is removed from the vacuum filter through ducts 9, 10 andchamber 13 in the direction shown by arrow B. Before the cell leaves thesuspension (cell 2d, FIGS. 4 and 6), duct 9 is closed by the partitionbetween the chambers, and the filtrate from cell 2 is removed only viaduct 9. This ensures complete filling of the space of cell 2a (FIGS. 4and 5), of accumulating pocket 12 (FIG. 5) and ofducts 9 and 10 (FIGS. 4and 5) with the filtrate. As soon as the cell emerges from thesuspension (cell 2b), duct 9 communicates through chamber 15 (FIGS. 1and 3) and valve 16 with the atmosphere, and duct 10 with overflowchannel 17 which, in turn, through cell 2 submerged in the suspension isconnected to the vacuum. Owing to the pressure difference appearing inducts 9 and 10, the filtrate is rapidly evacuated, and cell 2 is filledwith air (the direction of air flow is shown by arrow D in FIGS. 1, 2, 4and 5). The air in cell 2 upon passing through control valve 16 has apressure somewhat below atmospheric, which ensures the retaining of theprecipitates on the surface of drum 1.

After removal of the precipitate by means of device 5 (FIGS. I and 3),the cell submerges into the suspension (cell 2a, FIGS. 4 and 5). At thismoment duct 10 communicates with vacuum chamber 13 (FIGS. 1 and 3)through which the air is removed from cell 2. A rarefaction is createdin cell 2, and duct 9 of this cell is connected to overflow channel 17which, in turn, is connected to cell 2 emerging from the suspension(cell 2b, FIGS. 4 and 5) and filled with filtrate. Cell 2a is rapidlyfilled with the filtrate, after which the cell is ready for regenerationof the filtering material. Next cell 24 passes to the position of cell2c (FIGS. 4 and 6). Here cell 2 is connected either by both ducts 9 and10 or only by duct 10 (FIG. 6) to compressed air chamber 14. Thecompressed air supplied from chamber 14 into ducts 9 and 10 (arrow K inFIGS. 1 and 4) or only into duct 10 (arrow K, FIGS. 2 and 6) presses thefiltrate through the filtering material into trough 3 (FIGS. 1 and 3) ofthe filter. Thus regeneration of the filtering material is accomplishedin a small zone and with an insignificant amount of filtrate.

After regeneration of the filtering material, filtration proper begins,and the cycle is repeated. Owing to the fact that the drum is dividedinto a plurality of cells 2 functioning according to the cycle describedabove, continuous operation of the filter is ensured.

Owing to the rapid filling of the cell submerging into the suspensionwith the filtrate required for liquid regeneration of the filteringsurface, the vacuum filter provided by the invention has a considerablygreater working zone of filtration and, accordingly, a higher outputthan the known vacuum filters with liquid regeneration. It can besuccessfully used in the chemical, food, medicine, ore-concentration andother branches of industry for the separation of suspensions into theirsolid and liquid phases, and especially for the filtration of slime andother products which greatly clog the filtering material. I

What is claimed is:

l. A continuous drum vacuum filter comprising: a drum rotatable aboutits own axis; a trough for a suspension into which said drum is partlysubmerged; cells disposed on the working surface of said drum; filteringmaterial forming the external sides of said cells; a valve installedcoaxially with said drum; ducts so connecting said cells to the movablepart of said valve that said cells during rotation of said drum areconnected in the required sequence to suction and compressed airremoving the precipitate from the external surface of said drum.

2. A drum vacuum filter according to claim l, wherein said cells areprovided with accumulating pockets.

I0! 1* l W W

1. A continuous drum vacuum filter comprising: a drum rotatable aboutits own axis; a trough for a suspension into which said drum is partlysubmerged; cells disposed on the working surface of said drum; filteringmaterial forming the external sides of said cells; a valve installedcoaxially with said drum; ducts so connecting said cells to the movablepart of said valve that said cells during rotation of said drum areconnected in the required sequence to suction and compressed air lines;an overflow channel made in the fixed part of said valve and providingfor connection of said cell emerging from the suspension during rotationof said drum to said cell submerging into said suspension, therebyensuring overflowing of the filtrate from the former cell to the latterone; a device for removing the precipitate from the external surface ofsaid drum.
 2. A drum vacuum filter according to claim 1, wherein saidcells are provided with accumulating pockets.